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Mark the letter a, B, C, or D on your answer sheet to indicate the sentence that is closest meaning to each of the following questions or indicate the correct answer to each of them
It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species’ death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species. The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species become extinct at the same time- a mass extinction. One of the best- known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when appropriately 95 percent of all species died. Mass extinction can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the ocean. Such a change would probably lead to a mass extinction. One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth’s orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species’ survival may have nothing to do with its ability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.
The underlined word “ultimately” is closest in meaning to .............
Mark the letter a, B, C, or D on your answer sheet to indicate the sentence that is closest meaning to each of the following questions or indicate the correct answer to each of them
Tsunami is a Japanese word which means harbor wave and is used as the scientific term for seismic sea wave generated by an undersea earthquake or possibly an undersea landslide or volcanic eruption. When the ocean floor is tilted or offset during an earthquake, a set of waves is created similar to the concentric waves generated by an object dropped into the wave. Most tsunamis originate along the Ring of Fire, a zone of volcanoes and seismic activity, 32.500 km long that encircles the Pacific Ocean. Since 1819, about 40 tsunami have struck the Hawaiian Islands. A tsunami can have wave lengths, or widths, of 100 to 200 km, and may travel hundreds of kilometres across the deep ocean, reaching speeds of about 725 to 800 kilometres an hour. Upon entering shallow coastal waters, the wave, which may have been only about half a metre high out at sea, suddenly grows rapidly. When the wave reaches the shore, it may be 15 metres high or more. Tsunamis have tremendous energy because of the great volume of water affected. They are capable of obliterating coastal settlements. Tsunami should not be confused with storm surges, which are domes of water that rise underneath hurricanes or cyclones and cause extensive coastal flooding when the storms reach land. Storm surges are particularly devastating if they occur at high tide. A cyclone and accompanying storm surge killed an estimated 500,000 people in Bangladesh in 1970. The tsunami which truck south and southeast Asia in late 2004 killed over 200 thousand people.
What does the word concentric mean?
How to protect children Web fans from unsuitable material online while encouraging them to use the Internet has long been discussed in the US. For some parents, the Internet can seem like a jungle, filled with danger for their children. But jungles contain wonders as well as hazard and with good guides, some education, and a few precautions, the wilds of the Internet can be safely navigated. “Kids have to be online. If we tell our kids they can’t be allowed to surf the Internet, we’re cutting them off from their future,” said an expert. Most kids have started to use search engines. Many of them are great for finding tons of interesting Internet sites, and they can also locate places where you might not want your kids to go. There are search engines designed just for kids. A certain software contains only sites that have been selected as safe. The most popular way would be to use what is known as a “content screener”. But this can’t be wholly reliable, and the best thing parents can do is to talk to their kids and let them know what is OK or not OK to see or do on the Internet. Another way is that mum or dad is nearby when the child is surfing the Internet. A few other tips as follows: Don’t put the PC in a child’s room but keep it in an area where mum or dad can keep an eye on things. That also makes the Internet more of a family activity. Ask your child what he or she has been doing and about any friends they make online. Tell your child not to give online strangers personal information, especially like address and phone number. And tell your children never to talk to anyone they meet on line over the phone, send them anything, accept anything from them or agree to meet with them unless you go along.
The word “hazard” in the passage means ................